Authors

Abstract

The Pigeon River drains a 16,765-ha agricultural watershed in western Ottawa County, Michigan and discharges into south-central Lake Michigan. Extensive areas of wetlands in the upper watershed were drained in the 1920s, causing significantly altered hydrology characteristics by flashy discharges during storms and periods of snowmelt. We studied stream chemistry and hydrology for a four-year period between September, 1996, and October, 2000, to determine water quality status, to estimate annual nutrient exports, and to evaluate the effects of different seasonal flow types. Results of our study confirmed that the upper reaches of the Pigeon River experience chronically degraded water quality, with contributions from both nonpoint and point sources. As a result, the watershed has high annual rates of nutrient export (approximately 10.8 kg ha-1 inorganic N and 0.25 kg ha-1 PO4-P). With the influx of groundwater, change in land use to forest, and development of natural stream channel characteristics in the lower mainstream, water quality at baseflow in this section of the Pigeon River improves to the point where coldwater fish populations should persist. Inputs of degraded water during high flows, however, produce periods of environmental stress and the fish population in the lower Pigeon includes only a low number of pollution-tolerant, warmwater species. Large summer storms are biologically stressful because of increased temperatures and reduced dissolved oxygen levels, while spring storms and snowmelt contribute substantially to total nutrient suspended solids exports. Efforts to improve water quality in this and similar agricultural watersheds need to emphasize major reductions in the nonpoint source inputs through substantial improvements in land and water management practices. Wetland restoration and implementation of other stormwater retention practices in such watersheds also are required to reverse the acute impacts of high stormwater discharges caused by past drainage and steam channelization.